This invention relates to a method of operating a boom or jib (hereinafter called "a boom") which is mounted on a base, such as a tractor or wheeled vehicle such as are used on building sites and the like for the handling of loads, or a base which is fixed to or supported directly on the ground.
More particularly, the invention relates to a method of operating a boom which comprises an elongate member mounted on a base for pivotal movement about a first axis transverse to the axis of the elongate member, first fluid operated power means mounted between the base and the elongate member to control raising and lowering of the member about said first axis, an implement mounted at one end of the member for pivotal movement about a second axis transverse to the axis of the elongate member, second fluid operated power means comprising a double acting ram having a cylinder and plunger slidable therein, mounted between the implement and the member to control movement of the implement about the second axis, means to feed fluid under pressure to and from the first fluid operated power means along first feed lines via a first operating valve, means to feed fluid under pressure to and from the second fluid operated power means along second feed lines via second operating valve, a displacement means comprising a further double acting fluid operated ram connected between the member and the base to sense movement of the member about the first axis, fluid lines from the displacement means to the second fluid operated power means to transmit a signal to the second fluid operated power means to cause the second fluid operated power means to operate to maintain the orientation of the implement relative to the base as the implement is raised and lowered on the member. Such a boom will hereinafter be referred to as "of the kind specified".
Thus, where for example the implement is a pair of forks, a load supported on the forks can be maintained level relative to the base, for example, during raising and lowering.
Such booms are designed to handle loads up to a predetermined design limit. To increase the limit, it would be necessary to increase the capacity of at least the first fluid operated power means, which is not always practically possible due to restriction in available space.